Abandoned train tunnel?

Above Helen Hunt Falls, Manitou Springs, Colorado

The official trail ended at the brick formation seen at the top of the falls photo. I
hiked much further up the slippery mountain and was surprised to find a dirt road going
into this cave sealed off with a metal plate. Someone had used a cutting torch on the
plate, so I could see through to the other end of the tunnel a ways off, also with metal
plate.